1. Field of the Invention
The invention relates generally to electrical receptacles particularly suitable for receiving a device, such as a fluorescent lamp, having a pair of contact pins extending from the end thereof for connection with an electrical supply, and particularly to such receptacles having contact elements therein that are closed together only upon the disposition of a lamp in the receptacle.
2. Description of the Prior Art
It has been previously recognized that in certain types of installations for fluorescent lamps, such as those with dimming controls or in fixtures for three or more lamps, it is desirable or required that the primary circuit including the ballast for the fluorescent lamp open or become deenergized whenever a lamp is removed from the lampholder. The purpose of deenergizing the primary circuit is to reduce shock hazard during insertion or removal of lamps in those applications where the voltage from the lampholder contacts to ground exceeds a certain rating (presently 180 volts rms) or the available current to ground exceeds a rated current (now 5 milliamperes) at rated ballast supply voltage when measured through a 500 ohm resistor.
It is customary in such applications to incorporate, in the contact means for one of the lamp pins, a switching means that is operative to open a circuit with the removal of the lamp. Contact elements for such switching mechanisms have taken various forms in the past. They are generally characterized by including a first contact element that is movable upon the insertion of a lamp within the holder to be forced laterally into contact with a second contact element thus closing the operative circuit. The reliability with which the conductive contact is made or broken is affected by the configuration of the contact elements and their housing. Some elements may become deformed in use so that upon lamp removal there is insufficient resiliency to separate the contacts or upon reinsertion of the lamp there is insufficient resiliency to reclose the contacts. Other factors including, of course, the cost of the lampholder enter into the design of such a lampholder and it was with such various criteria in mind that the present invention came about.
In copending application Ser. No. 3077, filed Jan. 15, 1970, by the present inventor and assigned to the present assignee, now U.S. Pat. No. 3,654,587, issued Apr. 4, 1972, an improved fluorescent lampholder was disclosed that included contact members held in place by projections within a housing including a front and back portion but with a pin contacting portion that is flat and parallel with the front wall and prevented from twisting out of parallelism by such projections but with sufficient resilience for lateral motion upon lamp pin insertion. One of the design criteria that led to the present invention was the objective of providing a circuit interrupting fluorescent lampholder with interruptable contact elements compatible with such contact members for normal pin contacting as are described in the mentioned copending application.